Why do we choose local/seasonal food?
With the recent popularity of nutrition going back to our roots, it has become increasingly trendy to source locally grown produce (viva farmers’ markets). A lot of this has been driven by the perceived environmental effects of our current global agricultural system i.e. the ‘carbon footprint’ (I mean, should a tomato really need planes, trains and automobiles to make it to dinner?) - not to mention what this does to the cost of food. However we should also take time to address the moderate but very real nutritional benefits of eating local (and thus seasonal) food.
When fruit & veg are ripe, they are at their nutritional peak - picked too early (like when you have to transport across great distance) and they have fewer antioxidants (and some vitamins). Example: when picked ripe vs unripe, cherry tomatoes have higher levels of carotenoids (a key antioxidant). Modern preservation techniques (e.g. ethylene gas) offset some of the effects of early picking, but choosing stuff grown nearby usually means things will be picked at the right time i.e. healthier (and tastier).
After picking, nutrients degrade quite quickly - this means you should eat them as soon as you can. Example: 2 days after picking, spinach has up to 80% less vitamin C (leafy vegetables lose nutrients faster than more solid veg e.g. green beans). So, again - modern refrigeration/etc keep things as fresh as they can, but produce is still usually fresher i.e. healthier when it doesn’t have far to travel. [Sidenote: frozen vegetables are often superior to foods that have far to travel - the freezing usually keeps the nutrients stable.]